Sleep paralysis is a sleep disturbance that can be very troubling for the person experiencing it. The person appears to be fully awake but unable to move, and people often report feeling pressure on their chest and an overwhelming sense of dread. People often hallucinate in this state, most frequently seeing a figure next to, or at the end of the bed. This tends to only last a few minutes but can be a horrible experience. Some people are more prone to having sleep paralysis than others, especially if you have a condition that impacts your sleep such as narcolepsy. It has been poorly researched which accounts for the wide range of between 8-50% of the population being estimated to experience it at some point in their lives. It is estimated that about 5% of the population experiences it regularly.
Sleep paralysis is thought to account for some mythology - the idea of a succubus coming to someone in the night is thought to have come about from sleep paralysis. It also may account for some people's accounts of abduction. The mythology about the cause of sleep paralysis has shifted with our cultural ideas. In the 18th century the idea of a demon troubling your sleep was fairly normal, whereas now the idea of an alien abduction seems more plausible. This is an example of the kind of assumptions that our brains can reach for to explain a surreal and troubling experience.
There are treatments such as medications and CBT that have been shown to effect some improvement over the condition. However there is very little research into the overall efficacy of these treatments. Each culture around the world has its own mythologies around sleep paralysis demonstrating the importance of priming the brain to expect a cause of the experience such as the Jinn (evil genie) or an alien.